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Dry goods knowledge: HD monitoring how to choose the switch
Before a select switch <br> <br> selection switch according to the code stream and the number of cameras, we must first figure out how much bandwidth per channel images occupancy.
Take the early IPC example:
720P network camera, the main stream is 2 ~ 3M, sub-stream is 0.8 ~ 1M, a total of about 4M.
1080P network camera, the main stream is 4 ~ 6M, sub-stream is 0.8 ~ 1M, a total of about 7M.
Second, we must clarify the bandwidth capacity of the switch. Commonly used switches are fast switches and gigabit switches. Their actual bandwidth is generally only 60 to 70% of the theoretical value, so the available bandwidth of their ports is roughly 60Mbps or 600Mbps.
In terms of network topology, a LAN is usually a two-to-three-tier structure. Connect the camera to the access layer. Generally, a 100M switch is enough, unless you have a lot of cameras on one switch.
The aggregation layer and the core layer are calculated according to how many images are aggregated by the switch. The calculation method is as follows: If a 720P network camera is connected, generally within 15 lines of images, using a 100M switch; if more than 15 lines, use a gigabit switch; The 1080P network cameras are usually within 8 channels of images, with 100M switches, and more than 8 Gigabit switches.
Second, the choice of network monitoring switches required <br> <br> With the increasing use of high-definition video camera, how to choose the right, to meet the overall network infrastructure performance monitoring switch has become a program developed in the early HD monitoring system, Project quotations have a very important role. A suitable switch not only can play the function of monitoring the network and can effectively reduce the waste of resources.
The monitoring network has three layers of architecture: core layer, convergence layer, and access layer.
Take a 720P camera and use PoE power supply as an example, select the corresponding switch and connect the front-end switch every 20 720P to an access switch.
1, the conditional access select <br> <br> layer switches 1: Mary camera stream: 4Mbps, 20 cameras is 20 * 4 = 80Mbps.
In other words, the access port switch port must meet the 80Mbps/s transmission rate requirements, taking into account the actual transfer rate of the switch (usually 50% of the nominal value, 100M also about 50M), so the access layer switch Should use the switch with 1000M upload port.
Condition 2: The backplane bandwidth of the switch, for example, if a 24-port switch is selected, two 1000M ports are provided, and a total of 26 ports, then the bandwidth requirement of the switch backplane at the access layer is: (24*100M*2+1000*2*2) )/1000 = 8.8Gbps backplane bandwidth.
Condition 3: Packet Forwarding Rate: The packet forwarding rate of a 1000 M interface is 1.488 Mpps/s. Then, the switching rate of the switch at the access layer is: (24*100 M/1000 M+2)*1.488=6.55 Mpps.
Normally, we will call the switches that meet conditions 2 and 3 as wire-speed switches. For example, the Fengduda PS1024 or PS3024 will satisfy the wire-speed switching capability, and it is also a suitable access PoE switch in this case.
Based on the above conditions, when there are 20 720P cameras connected to a switch, the switch must have at least one 1000M uplink port and more than 20 100M access ports to meet the demand.
2, selection switch convergence layer <br> <br> or in the above example, if a total of five rich PS1024 access, the traffic aggregation layer: 80Mbps * 5 = 400Mbps, then the convergence layer uploaded The port must be above 1000M.
If five IPCs are connected to one switch, an 8-port switch is generally required. Then does the 8-port switch meet the requirements? You can see the following three aspects:
Backplane bandwidth: port number * port speed *2 = backplane bandwidth, ie 8*100*2=1.6Gbps
Packet exchange rate: port number * port speed / 1000 * 1.488 Mpps = packet exchange rate, ie 8 * 100/1000 * 1.488 = 1.20 Mpps. For some switches, the packet exchange rate is sometimes calculated to fail to meet this requirement. That is, non-line-speed switches are prone to delays when performing large-capacity throughput.
The bandwidth of the cascade port: the number of IPC streams* is the minimum bandwidth of the upload port, that is, 4.*5=20Mbps. In general, when the IPC bandwidth exceeds 45 Mbps, it is recommended to use a 1000M cascade port.
Third, how to choose the switch in network monitoring?
For example: There is a campus network, more than 500 high-definition cameras, stream 3 ~ 4 trillion, the network structure is divided into the core layer of the access layer convergence layer. Stored at the aggregation layer, each convergence layer corresponds to 170 cameras.
The problems faced: How to choose a product, the difference between Gigabit and Gigabit, what are the reasons that affect the transmission of images in the network, and what factors are related to the switch...
1, 2 times <br> <br> backplane bandwidth capacity of all ports and port number of x should be less than the nominal backplane bandwidth, non-blocking wire-speed full duplex exchange switch has proved maximum data exchange performance conditions of.
For example, a switch that can provide up to 48 Gigabit ports with a full configuration capacity of 48×1G×2=96Gbps can ensure non-blocking wire-speed packet switching when all ports are full-duplex. .
2, the packet forwarding rate <br> <br> full configuration packet forwarding rate (Mbps) = full configuration GE ports × 1.488Mpps + full configuration Mbps ports × 0.1488Mpps, wherein a Gigabit ports in the packet length word 64 The theoretical throughput of the festival is 1.488 Mpps.
For example, if a switch can provide up to 24 Gigabit ports and the advertised packet forwarding rate is less than 35.71 Mpps (24x1.488 Mpps = 35.71), then there is reason to believe that the switch is designed with a blocked architecture.
Generally, a switch that has both a backplane bandwidth and a packet forwarding rate is a suitable switch.
The switches with relatively large backplane and relatively small throughput not only retain the ability to upgrade and expand, but also have problems in the design of software efficiency/dedicated chip circuits. Switches with relatively small backplanes and relatively high throughput have relatively high overall performance.
The camera code stream affects the definition, which is usually the code stream setting of the video transmission (including coding and decoding capabilities of the code sending and receiving equipment, etc.). This is the performance of the front camera and has nothing to do with the network.
Usually the user thinks the clarity is not high, and it is actually a misunderstanding to think that the idea caused by the network causes.
In HD network video surveillance systems, there are often friends with feedback screen delays, stucks, etc. There are many reasons for this phenomenon, but in most cases the configuration of the switch is not reasonable enough, resulting in insufficient bandwidth.
Based on the above case, calculate:
Stream: 4Mbps
Access: 24*4=96Mbps<1000Mbps<4435.2Mbps
Convergence: 170*4=680Mbps<1000Mbps<4435.2Mbps
3, the main consideration <br> <br> access switch to access the link bandwidth between the convergence, i.e., the link capacity associated switch requires more than the number of simultaneously receiving a camera * rate. In this way, there will be no problem with real-time video recording. However, if a user sees the video in real time, the bandwidth needs to be taken into account. The bandwidth occupied by each user to view a video is 4 M. If each camera of an access switch is If one person is watching, the bandwidth of the camera *bit rate*(1+N) is needed, ie 24*4*(1+1)=128M.
4, convergence switch <br> <br> convergence layer 170 need to process camera 34M stream (170 * 4M = 680M), the aggregation switch means and forward the need to support more than 680M-exchange capacity. General storage is connected to the convergence, so video recording is wire-speed forwarding.
But to take into account real-time viewing of monitored bandwidth, each connection occupies 4M, and a 1000M link can support 250 cameras to be debugged. Each access switch connects 24 cameras. 250/24, the equivalent of the network can withstand the pressure of each camera at the same time 10 users in real-time viewing.
5, core switches <br> <br> core switches need to consider switching capacity and link bandwidth to converge, because storage is placed in the convergence layer, the core switch video is no pressure, that is as far as the number of people watching at the same time How much road video can be. Assume that in this case, there are 10 people watching at the same time. Each person sees 16 videos, that is, the exchange capacity needs to be greater than 10*16*4=640M.
6, switch to select video surveillance in focus <br> <br> LAN switch selection, select the access layer and aggregation layer switches typically only need to consider factors exchange capacity is enough, because users usually by a core switch Connect and get video.
In addition, because the main pressure is at the convergence layer switch, because it is necessary to bear the burden of monitoring the storage, but also bear the pressure of real-time viewing call monitoring, so it is very important to select the appropriate aggregation switch.
For the access switch, there is no essential difference between the ports that connect the cameras to the downstream ports at 100Mbit/Gigabit, but the uplink must be Gigabit.
If you have questions about the selection of network monitoring switches, you can contact us. Fengrunda is a leading global provider of transmission products & services. As long as you provide your monitoring scenarios and requirements, we can provide you with a variety of suitable switches (PoE switches, Ethernet switches, 10G switches, etc.) as well as improvements. a well-designed HD surveillance solution.
Dry goods knowledge: HD monitoring how to choose the switch
In HD network video surveillance systems, there are often friends who have feedback screen delays, stalls, etc. There are many reasons for this phenomenon, but in most cases the configuration of the switch is not reasonable enough, resulting in insufficient bandwidth.